Instruments and methods for manipulating a spinal fixation element

ABSTRACT

An instrument for manipulating a spinal fixation element relative to a bone anchor includes a bone anchor grasping mechanism, a first adjustment mechanism, and a second adjustment mechanism. The bone anchor grasping mechanism includes a first arm having a distal end configured to engage an opening provided in the bone anchor. The first adjustment mechanism includes a second arm pivotally connected to the first arm. The second arm has a distal end configured to engage an opening provided in the bone anchor and is operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm. The second adjustment mechanism is removably and replaceably coupled to the bone anchor grasping mechanism and is movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 11/756,318 filed May 31, 2007 (now U.S. Pat. No. 8,216,241),and entitled “Instruments and Methods for Manipulating a Spinal FixationElement,” which is a continuation-in-part of U.S. patent applicationSer. No. 11/143,099 filed Jun. 2, 2005 (now abandoned), and entitled“Instruments and Methods for Manipulating a Spinal Fixation Element,”both of which are hereby incorporated by reference in their entireties.

BACKGROUND

Spinal fixation systems may be used in orthopedic surgery to alignand/or fix a desired relationship between adjacent vertebrae. Suchsystems typically include a spinal fixation element, such as arelatively rigid fixation rod or plate or a relatively flexible tetheror cable, that is coupled to adjacent vertebrae by attaching the elementto various anchoring devices, such as hooks, bolts, wires, or screws.The spinal fixation element can have a predetermined contour that hasbeen designed according to the properties of the target implantationsite, and once installed, the spinal fixation element holds thevertebrae in a desired spatial relationship, either until desiredhealing or spinal fusion has taken place, or for some longer period oftime.

Spinal fixation elements can be anchored to specific portions of thevertebra. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a spinal fixation elementreceiving element, which, in spinal rod applications, is usually in theform of a U-shaped slot formed in the head for receiving the rod. Aset-screw, plug, cap or similar type of closure mechanism, is used tolock the rod into the rod-receiving portion of the pedicle screw. Inuse, the shank portion of each screw is then threaded into a vertebra,and once properly positioned, a fixation rod is seated through therod-receiving portion of each screw and the rod is locked in place bytightening a cap or similar type of closure mechanism to securelyinterconnect each screw and the fixation rod. Other anchoring devicesalso include hooks and other types of bone screws.

While current spinal fixation systems have proven effective,difficulties have been encountered in mounting rods, or other spinalfixation elements, into the rod-receiving portion of various fixationdevices. In particular, it can be difficult to align and seat the rodinto the rod receiving portion of adjacent fixation devices due to thepositioning and rigidity of the vertebra into which the fixation deviceis mounted. Thus, the use of a spinal rod approximator, also referred toas a spinal rod reducer, is often required in order to grasp the head ofthe fixation device, and reduce the rod into the rod-receiving portionof the fixation device.

While several rod approximators are known in the art, some tend to bedifficult and very time-consuming to use. Accordingly, there is a needfor an improved rod approximator and methods for seating a spinal rod ina rod-receiving portion of one or more spinal implants.

SUMMARY

Disclosed herein are instruments and methods for manipulating a spinalfixation element, such as a spinal rod, relative to a bone anchor, suchas a polyaxial or monoaxial bone screw. The instruments and methodsdisclosed herein are particularly suited for lateral and verticalalignment of a spinal fixation element relative to a bone anchor.

In accordance with one exemplary embodiment, an instrument formanipulating a spinal fixation element relative to a bone anchor maycomprise a bone anchor grasping mechanism, a first adjustment mechanismand a second adjustment mechanism. In the exemplary embodiment, the boneanchor grasping mechanism may include a first arm having a distal endconfigured to engage an opening provided in the bone anchor. The firstadjustment mechanism may include a second arm pivotally connected to thefirst arm. The second arm may have a distal end configured to engage anopening provided in the bone anchor and may be operable to adjust aspinal fixation element in a first direction upon pivoting relative tothe first arm. The second adjustment mechanism may be coupled to atleast one of the bone anchor grasping mechanism and the first adjustmentmechanism and may be movable relative to the bone anchor graspingmechanism to adjust the spinal fixation element in a second direction,perpendicular to the first direction, relative to the bone anchor.

In accordance with another exemplary embodiment, an instrument formanipulating a spinal fixation element relative to a bone anchor maycomprise a first arm, a second arm pivotally connected to the first arm,and adjustment mechanism coupled to the first arm and the second arm. Inthe exemplary embodiment, the first arm may have a distal end having anarcuate projection for engaging a first arcuate groove provided in thebone anchor. The second arm may have a distal end having an arcuateprojection for engaging a second arcuate groove provided in the boneanchor. The first arm and second arm may be pivotable about a pivot axisthat intersects the first arm and second arm and the second arm may beoperable to adjust a spinal fixation element in a first direction uponpivoting relative to the first arm. The adjustment mechanism may bemovable relative to the bone anchor grasping mechanism to adjust thespinal fixation element in a second direction, perpendicular to thefirst direction, relative to the bone anchor.

In accordance with another exemplary embodiment, an instrument formanipulating a spinal fixation element relative to a bone anchor maycomprise a first arm, a second arm pivotally connected to the first arm,an adjustment mechanism coupled to first arm and the second arm, and acoupling mechanism connected to the first arm and the second arm. Thefirst arm may have a distal end having a projection for engaging a firstopening provided in the bone anchor and the second arm may have a distalend having a projection for engaging a second opening provided in thebone anchor. The first arm and second arm may be pivotable about a pivotaxis that intersects the first arm and second arm and the second arm maybe operable to adjust a spinal fixation element in a first directionupon pivoting relative to the first arm. The adjustment mechanism may bemovable relative to the bone anchor grasping mechanism to adjust thespinal fixation element in a second direction, perpendicular to thefirst direction, relative to the bone anchor. The coupling mechanism maybe positioned between the first arm and the second arm such that thepivot axis intersects the coupling mechanism. The coupling mechanism maybe configured to receive the adjustment mechanism and permit motion ofthe adjustment mechanism relative to the first arm and the second arm.

In accordance with another exemplary embodiment, an instrument formanipulating a spinal fixation element relative to a bone anchor maycomprise a bone anchor grasping mechanism, a first adjustment mechanismand a second adjustment mechanism. In the exemplary embodiment, the boneanchor grasping mechanism may include a first arm having a proximal endwith a handle portion, a distal end configured to engage a firstreceiving portion provided on the bone anchor, and an intermediateportion disposed between the proximal and distal ends. The intermediateportion may have a housing with a threaded bore formed therein. Thefirst adjustment mechanism may include a second arm pivotally connectedto the housing of the first arm. The second arm may have a proximal endwith a handle portion and a distal end configured to engage a secondreceiving portion provided on the bone anchor. Furthermore, the secondarm may be operable to adjust a spinal fixation element in a firstdirection upon pivoting relative to the first arm. The second adjustmentmechanism may have a threaded portion configured to be removably andreplaceably coupled to the threaded bore of the housing of the first armand may be movable relative to the bone anchor grasping mechanism toadjust the spinal fixation element in a second direction, perpendicularto the first direction, relative to the bone anchor.

In accordance with another exemplary embodiment, an instrument formanipulating a spinal fixation element relative to a bone anchor maycomprise a first arm, a second arm pivotally connected to the first arm,a housing coupled to at least one of the first arm and the second arm,and an adjustment mechanism, which optionally can be removably andreplaceably coupled to the housing. In the exemplary embodiment, thefirst arm may have a proximal end with a handle portion and a distal endconfigured to engage a first receiving portion provided on the boneanchor. The second arm may have a proximal end with a handle portion anda distal end configured to engage a second receiving portion provided onthe bone anchor. The first arm and the second arm may be pivotable abouta pivot axis that intersects the first arm and the second arm and atleast one of the first arm and the second arm may be operable to adjusta spinal fixation element in a first direction upon pivoting relative tothe other arm. The housing may have a threaded bore formed therein. Theadjustment mechanism may have a threaded portion configured toselectively mate with the threaded bore of the housing and theadjustment mechanism may be movable relative to at least one of thefirst arm and the second arm to adjust the spinal fixation element in asecond direction that is generally perpendicular to the first direction,relative to the bone anchor.

BRIEF DESCRIPTION OF THE FIGURES

These and other features and advantages of the instruments and methodsdisclosed herein will be more fully understood by reference to thefollowing detailed description in conjunction with the attached drawingsin which like reference numerals refer to like elements through thedifferent views. The drawings illustrate principles of the instrumentsand methods disclosed herein and, although not to scale, show relativedimensions.

FIG. 1 is an assembly view of an exemplary embodiment of an instrumentfor manipulating a spinal fixation element relative to a bone anchor;

FIG. 2 is a front view of the instrument of FIG. 1;

FIG. 3 is a side view of the instrument of FIG. 1;

FIG. 4 is a top perspective view of the instrument of FIG. 1;

FIG. 5 is a side view of the distal end of the instrument of FIG. 1;

FIG. 6 is a side view in cross section of the distal end of theinstrument of FIG. 1;

FIG. 7 is a side view of another exemplary embodiment of an instrumentfor manipulating a spinal fixation element relative to a bone anchor;

FIG. 8 is a side view of another exemplary embodiment of an instrumentfor manipulating a spinal fixation element relative to a bone anchor,illustrating the lateral activation mechanism of the instrument;

FIG. 9 is a side view of another exemplary embodiment of an instrumentfor manipulating a spinal fixation element relative to a bone anchor,illustrating the coupling mechanism integrated into an arm of theinstrument;

FIG. 10 is a side view of an alternative exemplary embodiment of acoupling mechanism configured to permit motion of the adjustmentmechanism relative to the first arm and the second arm of theinstrument;

FIGS. 11A-11C are side views of alternative exemplary embodiments of thedistal end of the adjustment mechanism, illustrating alternativemechanisms for interacting with the spinal fixation element;

FIGS. 12A-12D are side views of alternative exemplary embodiments of thedistal end of the first arm of the instrument, illustrating alternativebone anchor engagement mechanisms;

FIG. 13 is a side view of the instrument of FIG. 1, illustrating theoperation of the instrument to adjust a spinal fixation element relativeto a bone anchor;

FIG. 14 is a front perspective view of another exemplary embodiment ofan instrument for manipulating a spinal fixation element relative to abone anchor;

FIG. 15A is a back perspective view of another exemplary embodiment ofan instrument for manipulating a spinal fixation element relative to abone anchor, with a second adjustment mechanism removed and in aposition where a rack is not engaged with a pawl;

FIG. 15B is a front perspective view of the instrument of FIG. 15A in aposition where the rack is engaged with the pawl;

FIGS. 15C and 15D are partial back and front perspective views of analternative embodiment of the instrument of FIG. 15A, illustrating analternative locking mechanism;

FIG. 16 is a top perspective view of the instrument of FIG. 15A;

FIG. 17 is a front perspective view of the second adjustment mechanismfor use with the instrument of FIG. 14;

FIG. 18 is a side perspective view of another exemplary embodiment of aninstrument for manipulating a spinal fixation element relative to a boneanchor with a separate adjustment mechanism disposed in a housing,illustrating the housing coupled to at least one of a first arm and asecond arm;

FIG. 19 is a top perspective view of the instrument of FIG. 18, with theseparate adjustment mechanism removed;

FIG. 20 is a front perspective view of the housing of the instrument ofFIG. 18, illustrating the coupling of the housing to one of the firstarm and the second arm; and

FIG. 21 is a front perspective view of the separate adjustment mechanismof the instrument of FIG. 18 which is configured to be removably andreplaceably coupled to the housing of the instrument of FIG. 18.

DETAIL DESCRIPTION OF EXEMPLARY EMBODIMENTS

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the instruments and methods disclosed herein.One or more examples of these embodiments are illustrated in theaccompanying drawings. Those of ordinary skill in the art willunderstand that the instruments and methods specifically describedherein and illustrated in the accompanying drawings are non-limitingexemplary embodiments and that the scope of the present invention isdefined solely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e. to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The terms “comprise,” “include,” and “have,” and the derivativesthereof, are used herein interchangeably as comprehensive, open-endedterms. For example, use of “comprising,” “including,” or “having” meansthat whatever element is comprised, had, or included, is not the onlyelement encompassed by the subject of the clause that contains the verb.

FIGS. 1-6 and 13 illustrate an exemplary embodiment of an instrument 10for manipulating a spinal fixation element 12, such as, for example, aspinal rod, a plate, a tether or cable or combinations thereof, relativeto a bone anchor 14, such as, for example, a bone screw or hook. Theexemplary instrument 10 is particularly suited adjust a spinal fixationelement in two directions relative to a bone anchor. For example, theexemplary instrument 10 is suited for both lateral adjustment of thespinal fixation element 12 and vertical adjustment of the spinalfixation element 12 relative to the bone anchor 14. The exemplaryinstrument 10 includes a bone anchor grasping mechanism 18 configured toengage an opening in the bone anchor 14, a first adjustment mechanism 20operable to adjust the spinal fixation element 12 in a first directionrelative to the bone anchor 14 and a second adjustment mechanism 22operable to adjust the spinal fixation element 10 in a second direction,at an angle to the first direction, e.g., perpendicular to the firstdirection, relative to the bone anchor 14.

As illustrated and in the description of the exemplary instrument 10that follows the spinal fixation element is a spinal rod 12 and the boneanchor is a monoaxial bone screw 14. One skilled in the art willappreciate that the spinal fixation element and the bone anchor are notlimited to the illustrated exemplary embodiments. The instrument may beused with any type of spinal fixation element and any type of boneanchor.

The bone anchor grasping mechanism 18 of the exemplary instrument 10 mayinclude a first arm 24 having a distal end 26 configured to releasablyengage a bone anchor. For example, the first arm 24 may be engaged to abone anchor in a manner that allows the first arm 24, and thus theinstrument 10, to be connected to the bone anchor 14 during use, e.g.,during adjustment of the spinal fixation element 12 relative to the boneanchor 14, and allows the first arm 24, and thus, the instrument 10, tobe disconnected from the bone anchor 14 at the conclusion of theprocedure. Preferably, the first arm 24 can be disconnected remotely.For example, the exemplary embodiment, the first arm 24 can bedisconnected from the bone anchor by manipulation of the proximal end ofthe first arm 24.

Referring to FIGS. 6, 12A and 12B, the distal end 26 of the first arm 24may be configured to engage an opening provided in the bone anchor 14.For example, the distal end 26 of the first arm 24 may include one ormore radially inward facing projection 28 that is sized and shaped toseat within an opening provided in a portion of the bone anchor. Thesize, shape and number of projections can be varied depending on, forexample, the opening(s) provided on the bone anchor and type ofconnection desired. In the illustrated exemplary embodiment, forexample, the projection 28 is generally arcuate in shape and has a crosssection and a curvature that is complementary to an arcuate groove 30provided in the spinal fixation element receiving member 32 of theexemplary bone anchor 14. Exemplary bone anchors having such featuresare described in U.S. patent application Ser. No. 10/738,286, filed Dec.16, 2003, incorporated herein by reference. In particular, theprojection 28 has a distal surface 36, a proximal surface 38, and agenerally radially facing connecting surface 40 that spans between thedistal surface 36 and the proximal surface 38, as shown in FIG. 12B. Inthe illustrated embodiment, the distal surface 36 is generally orientedperpendicular to the longitudinal axis L of the instrument 10 and theconnecting surface 40 is generally oriented parallel to the longitudinalaxis L of the instrument 10 and perpendicular to the distal surface 36.One or both of the proximal surface 38 and the distal surface 36 may beoriented at an angle other than perpendicular to the longitudinal axis Lof the instrument 10. For example, the proximal surface 38 may beoriented at an angle A to an orthogonal line 80, which is orientedperpendicular to the longitudinal axis L of the instrument 10. In theexemplary embodiment, the angle A may be approximately 5° toapproximately 30° and is preferably approximately 20°. The distalsurface 36 and the proximal surface 38 may be oriented at the same angleor, as in the exemplary embodiment, may be oriented at different angles.

In alternative embodiments, the distal end 26 of the first arm 24 mayinclude additional and/or alternatively positioned and/or shapedprojections. For example, the distal end 26 of the first arm 24 mayinclude a projection 28′ configured to engage a swaged openingpositioned between the proximal and distal ends of the spinal fixationelement receiving member 32 of the exemplary bone anchor 14, asillustrated in FIG. 12C. The projection 28′ may be generally cylindricalin shape, may be generally hemispherical in shape, or may have othersuitable shapes. In alternative embodiments, the distal end 26 mayinclude two projections, e.g., the arcuate projection 28 illustrated inFIGS. 12A and 12B and the projection 28′ illustrated in FIG. 12C. Inalternative embodiments, the distal end 26 of the first arm 24 may notinclude a projection. For example, the distal end 26 may be sized andshaped to engage the distal end of the of the spinal fixation elementreceiving member 32 of the exemplary bone anchor 14, as illustrated inFIG. 12D.

Continuing to refer to FIGS. 1-6 and 13, in the exemplary instrument,the first adjustment mechanism 20 may include a second arm 50 that ispivotally connected to the first arm 24 and is operable to adjust thespinal fixation element 12 in a first direction upon pivoting of thesecond arm 50 relative to the first arm 24. For example, the first arm24 may be directly pivotally connected to the second arm 50 such thatthe first arm 24 and the second arm 50 pivot about a pivot axis 52 thatintersects the first arm 24 and the second arm 50. In alternativeembodiments, the first arm 24 may be indirectly pivotally connected tothe second arm 50, for example, the first arm 24 may be off set from thesecond arm 50 such that the first arm 24 and the second arm 50 pivotabout a pivot axis that does not intersect both the first arm 24 and thesecond arm 50.

The second arm 50 may have a distal end 56 configured to releasablyengage the bone anchor 14. The distal end 56 of the second arm 50 may beconfigured in a manner analogous to the distal end 26 of the first arm24. For example, the distal end 56 of the second arm 50 may include aprojection 58 sized and shape to engage an opening in the bone anchor14.

The inner surface 60 of the second arm 50 of the exemplary instrument 10may be configured to facilitate contact with and adjustment of thespinal fixation element 12 relative to the bone anchor. For example, theinner surface 60 of the second arm 50 may be coated with a materialhaving a relatively low coefficient of friction to facilitate movementof the spinal fixation element 12 along the inner surface 60 of thesecond arm 50 during adjustment of the spinal fixation element in thefirst direction.

Continuing to refer to FIGS. 1-6 and 13, the second adjustment mechanism22 may be coupled to the first arm 24 and/or the second arm 50 and maybe movable relative to the first arm 24 and/or the second arm 50 toadjust the spinal fixation element 12 relative to the bone anchor 14 ina second direction that is different to, e.g., at an angle to, the firstdirection. In the illustrated embodiment, the second adjustmentmechanism 22 comprises an elongated tubular body 60 having a proximalend 62 and a distal end 64 and a lumen 66 extending between the proximalend 62 and the distal end 64. The lumen 66 may be sized and shaped topermit a closure mechanism delivery instrument 90 to be positionedtherethrough. The closure mechanism delivery instrument 90 is providedfor the delivery of a closure mechanism 92, for example, a set screw orthe like, to the bone anchor 14 to secure the spinal fixation element 12relative to the bone anchor 12 after alignment of the spinal fixationelement 12. In the illustrated embodiment, the closure mechanismdelivery instrument 90 is a screwdriver having a distal end 94 withexternal threads for engaging the closure mechanism 92.

The distal end 64 of the tube 60 may indirectly or directly contact thespinal fixation element 12 to adjust the spinal fixation element 12 inthe second direction. For example, in the illustrated embodiment, thetube 60 may be advanced with the closure mechanism delivery instrument90 and the closure mechanism 92 may be positioned distal to the distalend 64 of the tube 60, as illustrated in FIGS. 11B and 13. In suchembodiments, the closure mechanism 92 may contact the spinal fixationelement 12 and, thus, the tube 60 may adjust the spinal fixation element12 through the closure mechanism 92. In alternative embodiments, thedistal end 64 of the tube 60 may directly contact the spinal fixationelement 12 to effect adjustment of the spinal fixation element 12, asillustrated in FIG. 11C. In certain embodiments, the distal end 64 ofthe tube may be sized and shaped to facilitate contact with the spinalfixation element 12. For example, the distal end 64 may be forked orbifurcated to engage the spinal fixation element 12 on opposing sides,as illustrated in FIG. 11A. In such embodiments, the distal end 64 mayhave an arcuate contact surface 68 having a curvature approximate to thecurvature of the spinal fixation element 12.

The exemplary instrument 10 may include a coupling mechanism 100 that isconnected to the first arm 24 and/or the second arm 50 and is configuredto receive the second adjustment mechanism 22, e.g., tube 60, and permitmotion of the second adjustment mechanism 22 relative to the first arm24 and/or the second arm 50. In the illustrated embodiment, for example,the coupling mechanism 100 is a collar or nut 102 having internalthreads 104 that may engage external threads 70 provided on the tube 60between the proximal end 62 and the distal end 64 of the tube 60.Rotation of the tube 60 relative to the collar 102 causes the tube 60 toadvance distally or proximally, depending on the direction of rotation,relative to the first arm 24 and the second arm 50. The tube 60 may beprovided with a handle 72 at the proximal end 62 of the tube 60 tofacilitate gripping and rotation of the tune 60.

The collar 102 may be connected to the first arm 24 and/or the secondarm 50 anywhere along the length of the arm(s). In the illustratedembodiment, for example, the collar 102 is connected to and positionedbetween the first arm 24 and the second arm 50. The collar 102 may bepositioned between the proximal and distal ends of the first arm 24 andthe second arm 50 proximate the area in which the arms intersect. In theillustrated embodiment, for example, the collar 102 is positioned suchthat the pivot axis 52 intersects the collar 102.

In alternative embodiments, the collar 102 may be integral to the firstarm 24 and/or the second arm 50. Referring to FIG. 9, for example, thecollar 102 may be integral to the second arm 50 of the instrument 10.Alternatively, the collar 102 may be integral to the first arm 24 or beformed by both the first arm 24 and the second arm 50.

In alternative embodiments, the collar 102 may be configured to allowthe tube 60 to advance distally without rotation. For example, thecollar 102 may include a threaded member 106 that is movable in adirection perpendicular to the tube 60 to allow the threaded member 106to selectively engage the threads 70 on the tube 60, as illustrated inFIG. 10. In the illustrated embodiment, the threaded member 106 ismovable between a first position in which the threaded member 106engages the external threads 70 in the tube 60, as illustrated in FIG.10, and a second position in which the threaded member 106 disengagesthe external threads 70 on the tube 60 to permit axial motion of thetube 60 without rotation. In this manner, the tube 60 may be quicklyadvanced, without the need for rotation, into contact with the spinalfixation element 12. Upon engagement with the spinal fixation element12, the tube 60 may be rotated to engage the threaded 70 on the tube 60with the threads of the threaded member 106 and, thus, further advancethe spinal fixation element 12. The collar 106 may include one or moresprings 108 that bias the threaded member 106 into engagement with thethreads 70 of the tube 60, i.e., the first position. The teeth 110 ofthe threaded member 106 may include an angled flank 112 that facilitatestranslation of the threaded member 106 from the first position to thesecond position.

The exemplary instrument 10 may include an activation mechanism 120coupled to the bone anchor grasping mechanism 18 and to the firstadjustment mechanism 20 to effect relative motion of the first arm 24and the second arm 50. For example, the activation mechanism 120 maycomprise a first handle 122 connected and proximal to the first arm 24and a second handle 124 connected and proximal to the second arm 50. Thefirst handle 122 may be pivotally connected to the second handle 124.Motion of the first handle 122 and the second handle 124 towards oneanother causes the distal end 26 of the first arm 24 to move toward thedistal end 56 of the second arm 50. The activation mechanism 120 mayinclude a spring or the like positioned between the first handle 122 andthe second handle 124 to bias the first handle 122 and the second handle124 to an open, separated position. The activation mechanism 120 mayalso include a locking mechanism, such as a latch or a ratchet assembly,that is operable to lock the handles 122, 124 in position relative toone another, for example, in a closed position to retain the bone anchorbetween the distal ends 26, 56 of the arms 24, 50.

Although the exemplary activation mechanism 120 includes two handles122, 124, in other exemplary embodiments, the activation mechanism 120may include additional pivotally connected linkages to increase themechanical advantage provided by the activation mechanism.

In the exemplary embodiment, the handles 122, 124 of the activationmechanism 120 are oriented generally in a direction parallel to thelongitudinal axis L of the instrument 10. In alternative embodiments,the activation mechanism 120 may comprise a fixed handle 130 and amovable handle 132 that is pivotally connected to the fixed handle 130at a pivot point 134 proximal to the pivot axis 52 of the first arm 24and the second arm 50, as illustrated in FIG. 7. In the exemplaryembodiment illustrated in FIG. 7, motion of the movable handle 132toward the fixed handle 130 causes the causes the distal end 66 of thesecond arm 50 to move toward the distal end 26 of the first arm 24. Themovable arm 132 may be connected to the second arm 50 by one or morepivotally connected linkages.

In alternative embodiments, the one or more of the handles of theactivation mechanisms 120 may be laterally oriented relative to thelongitudinal axis L of the instrument 10. Referring to FIG. 8, forexample, a movable handle 132 and a fixed handle 130 may be orientedlateral to, e.g., at angle to, the longitudinal axis L of the instrument10. In the embodiment illustrated in FIG. 8, for example, the movablehandle 132 and the fixed handle 130 are oriented generally perpendicularto the longitudinal axis L of the instrument 10.

The components of the exemplary instrument 10 may be made from anymaterial suitable for use in vivo, including, for example, metals suchas stainless steel and titanium, polymers, or composites thereof. Thecomponents of the exemplary instrument 10 may be constructed of the sameor different materials.

In use, the exemplary instrument 10 may be employed to adjust theposition of a spinal fixation element 12 in multiple directions relativeto a bone anchor. Referring to FIG. 13, the distal end 26 of the firstarm 24 may be engaged with the bone anchor 14. By moving the secondhandle 122 toward the first handle 124, in the direction of arrow A, thedistal end 56 of the second arm 50 is pivoted about the pivot axis 52and moved in the direction of the distal end 26 of the first arm 24 andthe bone anchor 14, as indicated by arrow B. As the second arm 50 movestoward the bone anchor 14, the inner surface 60 of the second arm 50engages the spinal fixation element 12 to move the spinal fixationelement 12 in a first direction, indicated by arrow C, toward the boneanchor 14. This is generally referred to as lateral approximation of thespinal fixation element 12.

Upon vertical alignment of the spinal fixation element 12 with thelongitudinal axis L of the instrument and the bone anchor, the tube 60may be advanced distally in a second direction into contact with spinalfixation element 12, as indicated by arrow D. Further advancement of thetube 60 toward the bone anchor 14 advances the spinal fixation element12 toward the bone anchor 14 until the spinal fixation element 12 isseated in the bone anchor 14. The delivery instrument 90 may used toengage the closure mechanism 92 with the bone anchor 14 and secure thespinal fixation element 12 to the bone anchor 14.

FIGS. 14-17 illustrate another alternative embodiment of an instrument210 for manipulating a spinal fixation element, which is particularlysuited to adjust a spinal fixation element in two directions relative toa bone anchor. For example, the instrument 210 is suited for bothlateral adjustment of the spinal fixation element and verticaladjustment of the spinal fixation element relative to the bone anchor.The instrument 210 includes a bone anchor grasping mechanism 218configured to engage a first receiving portion of the bone anchor in themanner described above in connection with other embodiments asillustrated in FIGS. 2-6, 12A-12D, and 13. Instrument 210 also includesa first adjustment mechanism 220 operable to adjust the spinal fixationelement in a first direction relative to the bone anchor, and a secondadjustment mechanism 222 operable to adjust the spinal fixation elementin a second direction, at an angle to the first direction, e.g.,generally perpendicular to the first direction, relative to the boneanchor. As will be described below, the first adjustment mechanism 222can have first and second arms 224, 250 that are connected together at apivot and which are operable in a pliers-like manner.

As illustrated and in the description of the instrument 210 thatfollows, the spinal fixation element is a spinal rod 12 and the boneanchor is a monoaxial bone screw 14 as described above in connectionwith other embodiments. However, one skilled in the art will appreciatethat the spinal fixation element and the bone anchor are not limited tothe illustrated embodiments and that the instrument may be used with anytype of spinal fixation element and any type of bone anchor.

Referring to FIGS. 14-16, the bone anchor grasping mechanism 218 of theinstrument 210 may include a first arm 224 having a proximal end 225with a handle portion 221, a distal end 226 configured to releasablyengage the bone anchor, and an intermediate portion 227 disposed betweenthe proximal end 225 and the distal end 226. The first arm 224 mayengage and disengage a bone anchor in a manner similar to the mannerdescribed above for the first arm 24 of the instrument 10, or in anyother manner known to one skilled in the art.

In one embodiment of the instrument 210, the handle portion 221 of thefirst arm 224 may include features that would assist in the comfort andease of use of the instrument 210. Any number of features could beincluded to provide such comfort and ease of use. In one embodimentillustrated in FIGS. 15A, 15B, and 16, the first arm 224 includes fingergrips 217, which are represented by contours or depressions formed inthe handle portion 221. In an alternative embodiment, the finger grips217 and/or the handle portion 221 may be cushioned. In yet anotherembodiment, the proximal end 225 of the first arm 224 may include afinger stop 219. As illustrated in FIGS. 15A, 15B, and 16, the fingerstop 219 is formed by a flange or lateral extension and eases use byassisting in locating the proximal end 225 of the first arm 224. Oneskilled in the art will appreciate that a variety of different featuresto assist in the comfort and ease of use of the instrument 210 can beused, and that the examples of finger grips and a finger stop are merelytwo examples.

In yet another embodiment, the distal end 226 of the first arm 224 maybe configured to engage a first receiving portion provided in the boneanchor. For example, the distal end 226 of the first arm 224 may includeone or more radially inward facing projections 228 that are sized andshaped to seat within the first receiving portion provided in the boneanchor, e.g., as shown in FIG. 6. In another embodiment, the bone anchormay contain multiple receiving portions, such that the distal end 226 ofthe first arm 224 includes multiple projections 228 to engage themultiple receiving portions.

In an exemplary embodiment, the intermediate portion 227 may include ahousing 229, which can have a threaded bore 231 formed therein. Thehousing may be oriented in a plane that is generally transverse to theorientation of the first arm 224, and one or more alignment slots 233may be formed in the housing 229 in communication with the threaded bore231. The shape of the alignment slots 233 may vary as long as they forma shape that is effective to assist in aligning the second adjustmentmechanism 222 with the bone anchor grasping mechanism 218 to facilitatecoupling of the second adjustment mechanism 222 to the threaded bore 231as will be described below. A further alignment feature may be providedon an inner portion of the first and/or second arm 224, 250 in the formof an alignment groove 237 that is in communication with the alignmentslot 233 of the housing 229. In one embodiment, both the first andsecond arms 224, 250 include the alignment groove 237. It is envisionedthat any number of alignment grooves 237 can be used in the instrument210. It is also envisioned that the shape of the alignment grooves 237is not limited to the shape illustrated in FIGS. 14-16, but rather theshape can be any shape that assists in maintaining alignment of thesecond adjustment mechanism 222 with the bone anchor grasping mechanism218 as it moves relative to the first adjustment mechanism 220.

The first adjustment mechanism 220 also includes a second arm 250 thatis pivotally connected to the housing 229 of the first arm 224 and thatis operable to adjust the spinal fixation element in a first directionupon pivoting of the second arm 250 relative to the first arm 224. Forexample, the first arm 224 may be directly pivotally connected to thesecond arm 250 such that the first and second arms 224, 250 pivot abouta pivot axis 252 that intersects the first and second arms 224, 250. Inalternative embodiments, the first and second arms 224, 250 may pivot inalternative manners, such as those manners described above andillustrated in FIGS. 7 and 8 for the instrument 10.

The second arm 250 may include a proximal end 255 with a handle portion251 and a distal end 256 configured to releasably engage the boneanchor. In alternative embodiments, any feature that would assist in thecomfort and ease of use of the instrument 210, such as the finger grips217 and the finger stop 219 provided on the first arm 224 as describedabove, may also be provided on the second arm 250. Additionally, thedistal end 256 of the second arm 250 may be configured in a manneranalogous to the distal end 226 of the first arm 224. For example, thedistal end 256 of the second arm 250 may include a projection 258 thatis sized and shaped to engage a second receiving portion in the boneanchor. In another embodiment, the bone anchor may contain multiplereceiving portions, such that the distal end 256 of the second arm 250includes the multiple projections 258 to engage the multiple receivingportions. Furthermore, the distal end 226 of the first arm 224 and/orthe distal end 256 of the second arm 250 may include features that allowfor easier and more precise movement of the spinal fixation elementrelative to the bone anchor. In one embodiment the feature is a guidingportion 257 (FIG. 15A) that is angled toward the other of the first arm224 and the second arm 250 respectively. It is envisioned that anynumber of features that provide for easier and more precise movement ofthe spinal fixation element relative to the bone anchor may beincorporated to the distal ends 226, 256 of the first and second arms224, 250, respectively.

In one aspect, the instrument 210 can be constructed such that one orboth of the first and second arms 224, 250 are sufficiently thin so asto create an inherent flexibility within the first and second arms 224,250. This design enables the first and second arms 224, 250 to storepotential energy as a result of a further closure force applied toeither or both of the handle portions 221, 251 after the distal ends226, 256 of the first and second arms 224, 250, respectively, areengaged with the bone anchor. In one embodiment, the handle portion 251of the second arm 250 is able to move a distance in the range ofapproximately 5 to 10 millimeters toward the handle portion 221 of thefirst arm 224 after the distal ends 226, 256 of the first and secondarms 224, 250, respectively, are engaged with the bone anchor. Oneskilled in the art will appreciate that in alternative embodiments, thehandle portion 221 of the first arm 224 may be able to move a distancein the range of approximately 5 to 10 millimeters toward the handleportion 254 of the second arm 240, or alternatively, that both handleportions 221, 251 may be able to move a distance in the range of 5 to 10millimeters toward each other after the distal ends 226, 256 of thefirst and second arms 224, 250, respectively, are engaged with the boneanchor. One skilled in the art will appreciate that the first and secondarms 224, 250 can be constructed in a variety of different ways, andwith differing relative dimensions, to achieve such desired flexibility.For example, the thickness of the arms can be greater at a distal endand gradually decrease in the proximal direction. In one embodiment, thefirst and second arms 224, 250 are constructed such that the thicknessof the arms at their distal ends is approximately 5 mm, the thickness ofthe arms at an intermediate portion is approximately 4 mm, and thethickness of the arms at their proximal ends is approximately 3 mm.

One skilled in the art will appreciate that it is possible to createsuch inherent flexibility in the instrument 210 in other ways as well.For instance, by way of a non-limiting example, and as shown in FIGS.15A, 15B, and 16, a channel 243 and a channel 253 may be disposed on aninner surface 241 of the first arm 224 and an inner surface 251 of thesecond arm 250, respectively. Similar to sufficiently thin arms, thechannels 243, 253 both create an inherent flexibility within the firstand second arms 224, 250, respectively, such that the first and secondarms 224, 250 are enabled to store potential energy as a result of afurther closure force applied to either or both of the handle portions221, 251 after the distal ends 226, 256 of the first and second arms224, 250, respectively, are engaged with the bone anchor. Only onechannel 243, 253 is necessary to create inherent flexibility in theinstrument 210. One skilled in the art will appreciate that the size andshape of channels 243, 253 may vary as long as they are of a size and/orshape that assists in creating inherent flexibility.

The bone anchor grasping mechanism 218 may include a biasing mechanism300 configured to bias at least one of the handle portions 221, 251 ofthe first and second arms 224, 250, respectively, to either an openposition or a closed position. In one embodiment, the biasing mechanism300 may be disposed between the handle portions 221, 251. In anotherembodiment, the biasing mechanism 300 may be disposed between theintermediate portion 227 of the first arm 224 and the second arm 250.The biasing mechanism 300 can take a variety of forms, but in oneembodiment it is a leaf spring. In another embodiment, the biasingmechanism 300 may have a central opening 302 formed therein that isconfigured to permit passage of the second adjustment mechanism 222therethrough. In yet another embodiment, the biasing mechanism 300 mayinclude two or more components which cooperate with one another to formthe biasing mechanism 300. One skilled in the art will appreciate that avariety of different biasing mechanisms can be used with the bone anchorgrasping mechanism 218, and that the example of a leaf spring is merelyone example.

In addition to including the biasing mechanism 300, the bone anchorgrasping mechanism 218 may also include a locking mechanism 280 coupledto the handle portion 251 of the second arm 250 that is effective tomaintain the handle portions 221, 251 in a desired position relative toone another. FIGS. 15A and 15B illustrate one example of a lockingmechanism 280 that includes a rack 282, with teeth 283 formed therein,that is pivotally mounted on the handle portion 251 of the second arm250 such that the rack 282 extends towards the first arm 224. In thisembodiment, a pawl 284 may be formed on the handle portion 221 of thefirst arm 224 such that the rack 282 is able to selectively engage theteeth 283 with the pawl 284 to resist the force of the biasing mechanismand thus maintain a desired position of the handle portions 221, 251.

Various design modifications are possible. For example, the teeth 283may be recessed in order to prevent undesired cutting of items such assurgical gloves. Further, when the rack 282 is selectively disengagedfrom the pawl 284, it may be pivotably oriented at an angle other thanzero relative to a plane of the handle portions 221, 251. One skilled inthe art will appreciate that the locking mechanism 280 could be coupledto either of the handle portions 221, 251.

Just as the locking mechanism 280 may be coupled to either of the handleportions 221, 251, the locking mechanism 280 may also be coupled to anyportion of either the first or second arm 224, 250, including theintermediate portion 227 of the bone anchor grasping mechanism 218.

FIGS. 15C and 15D illustrate an embodiment of the bone anchor graspingmechanism 218 with an alternative locking mechanism 280′. Asillustrated, locking mechanism 280′ includes a bar 292 coupled to thefirst arm 222 and extending towards the second arm 250. A latch 294 iscoupled to the second arm 250 such that the latch 294 can selectivelyengage the bar 292 at various locations across the bar 292 to maintainthe handle portions 221, 251 in a desired position relative to oneanother. A person skilled in the art would recognize that in alternativeembodiments, components of the locking mechanisms 280 and 280′ such asthe rack 282, the pawl 284, the bar 292, and the latch 294 may belocated anywhere on the first or second arm 224, 250, depending on thedesired operation of the bone anchor grasping mechanism 218. One skilledin the art also will appreciate that a bone anchor grasping mechanismutilizing a rack and a pawl and a bone anchor grasping mechanismutilizing a bar and a latch are just two of many different lockingmechanisms that could be used to maintain the handle portions 221, 251in a desired position relative to one another.

Now referring to FIGS. 14 and 17, the second adjustment mechanism 222may have a threaded portion 223 formed over at least a portion thereofthat is configured to be removably and replaceably mated with thethreaded bore 231 of the housing 229. In one embodiment the threadedportion 223 is disposed on an intermediate portion of the secondadjustment mechanism 222. The second adjustment mechanism 222 can alsoinclude an alignment feature 235 that is distal to the threaded portion223 and configured to fit within the alignment slot 233 of the housing229 and the alignment groove 237 of the first or second arm 224, 250.The alignment feature can be one or more projections formed on an outersurface of the second adjustment mechanism 222 that is able to fitwithin the alignment slot(s) 233 and the alignment groove(s) 237. In oneembodiment, the alignment feature 235 may be a fin, but it can also be apin or other protruding structure capable of communicating with thealignment slot(s) 233 and the alignment groove(s) 237. While FIG. 17illustrates the second adjustment mechanism 222 having two opposedalignment features 235, it is envisioned that one or more than twoalignment features 235 can be present on the second adjustment mechanism222.

The second adjustment mechanism 222 may also be movable relative to thefirst and/or second arm 224, 250 to adjust the spinal fixation elementrelative to the bone anchor in a second direction that is different to,e.g., at an angle to, the first direction. In use, the second adjustmentmechanism 222 can be aligned for placement within the threaded bore 231.When a biasing mechanism such as the biasing mechanism 300 as shown inFIG. 14 is present, the second adjustment mechanism passes through thecentral opening 302 and into the threaded bore 231. To pass through thethreaded bore 231, the alignment feature 235 must be aligned with thealignment slot(s) 233 and the alignment groove(s) 237. The secondadjustment mechanism 222 can be advanced through the threaded bore 231without rotation until the threaded portion 223 abuts threads of thethreaded bore 231. Thereafter, rotation of the second adjustmentmechanism 222 allows the threads to mate and further distally advancethe second adjustment mechanism 222. The engagement of the threadedportion 223 within threaded bore 231 maintains alignment of the secondadjustment mechanism 222 during an initial phase of its distaladvancement. The interaction of the alignment feature 235 and thealignment groove(s) 237 maintains alignment upon further distaladvancement. One skilled in the art will appreciate that because thesecond adjustment mechanism 222 is removable, the bone anchor graspingmechanism 218 and the second adjustment mechanism 222 may be used eitherindependently or together.

FIGS. 18-21 illustrate an alternative embodiment of an instrument 310for manipulating a spinal fixation element, which is particularly suitedto adjust a spinal fixation element in two directions relative to a boneanchor. For example, the instrument 310 is suited for both lateraladjustment of the spinal fixation element and vertical adjustment of thespinal fixation element relative to the bone anchor. The instrument 310,which has a forceps-like configuration, includes a first arm 324configured to engage a first receiving portion in the bone anchor in themanner described above in connection with other embodiments asillustrated in FIGS. 2-6, 12A-12D, and 13. Instrument 310 also includesa second arm 350 pivotally connected to the first arm 324 such that atleast one of the first arm 324 and the second arm 350 may be operable toadjust the spinal fixation element in a first direction relative to thebone anchor, a housing 329 coupled to at least one of the first andsecond arms 324, 350, and a separate adjustment mechanism 322 operableto adjust the spinal fixation element in a second direction, at an angleto the first direction, e.g., generally perpendicular to the firstdirection, relative to the bone anchor.

As illustrated and in the description of the instrument 310 thatfollows, the spinal fixation element is a spinal rod 12 and the boneanchor is a monoaxial bone screw 14. One skilled in the art willappreciate that the spinal fixation element and the bone anchor are notlimited to the illustrated embodiments. The instrument may be used withany type of spinal fixation element and any type of bone anchor.

Referring to FIGS. 18-20, the first arm 324 may include a proximal end325 with a handle portion 321 (e.g., a finger or thumb loop) and adistal end 326 configured to releasably engage the bone anchor. Thefirst arm 324, and in particular the distal end 326, may engage anddisengage a bone anchor in a manner similar to the manner describedabove for the instrument 10, or in any other manner known to one skilledin the art.

The second arm 350 may be pivotally connected to the first arm 324 andat least one of the first and second arms 324, 350 is operable to adjustthe spinal fixation element in a first direction upon pivoting relativeto the other arm. For example, the first arm 324 may be directlypivotally connected to the second arm 350 such that the first and secondarms 324, 350 pivot about a pivot axis 352 that intersects the first andsecond arms 324, 350. The first and second arms 324, 350 may pivot inalternative manners, such as those manners described above andillustrated in FIGS. 7 and 8 for the instrument 10.

The second arm 350 may include a proximal end 355 with a handle portion351 (e.g., a finger or thumb loop) and a distal end 356 configured toreleasably engage the bone anchor. The distal end 356 of the second arm350 may be configured in a manner that is analogous to the distal end326 of the first arm 324 and similar to the distal end 256 of theinstrument 210, including features such as a receiving portion(s) and aguiding portion 357 that is configured and operates similar to theangled guiding portion 257 of the instrument 210. Similarly, the firstand/or second arms 324, 350, may be manufactured in a manner similar tothat described above for the first and second arms 224, 250 to create aninherent flexibility within the first and second arms 324, 350 asdescribed above.

As shown in FIGS. 18-20, the first and second arms 324, 350 each have asomewhat curved structure such that the distal ends 326, 356 of thefirst and second arms 324, 350 are longitudinally offset from theproximal ends 325, 355 of the first and second arms 324, 350. Meanwhile,the housing 329 is coupled to at least one of the first and second arms324, 350 and may include a threaded bore 331. In one embodiment, thehousing 329 is positioned alongside and offset from a longitudinal axisof the proximal ends 325, 355 of the first and second arms 324, 350. Inaddition, the housing is proximal to and longitudinally aligned with thedistal ends 326, 356 of the first and second arms 324, 350. Such anorientation creates an alignment such that a longitudinal axis M runningthrough a center of the threaded bore 331 extends between the distalends 326, 356 of the first and second arms 324, 350, and is generallyparallel to at least one of the handle portions 321, 351.

The components of the housing 329 are similar to the housing 229 of theinstrument 210 in that the housing 329 includes one or more alignmentslots 333 similar to the alignment slots 233 described above. Furtheralignment may be provided in the housing 329 by an alignment groove 337in communication with the alignment slot 333 of the housing 329. In oneembodiment, the alignment groove 337 is contained in an extension 339 ofthe housing 329. It is envisioned that any number of the alignmentgrooves 337 can be used in the instrument 310, and furthermore that thelocation of the alignment grooves 337 may be varied depending on theparticular design of the instrument 310. It is also envisioned that theshape of the alignment grooves 337 is not limited to the shapeillustrated in FIGS. 18-20, but rather the shape can be any shape thatassists in aligning the adjustment mechanism 322 with the housing 329.

Although not illustrated, it is envisioned that a biasing mechanismsimilar to the biasing mechanism 300 of the instrument 210 may bedisposed between at least one of the first and second arms 324, 350 tobias at least one of the arms in either an open position or a closedposition. Similarly, it is envisioned that a locking mechanism similarto the locking mechanisms 280 and 280′ of the instrument 310 may bedisposed between the first and second arms 324, 350 to maintain thehandle portions 321, 351 in a desired position relative to one another.In one embodiment, a locking mechanism 380 may be coupled to either orboth of the handle portions 321, 351 and may be effective to maintainthe handle portions 321, 351 in a desired position relative to oneanother. The locking mechanism 380 may include a first bar 382 and asecond bar 384 opposed to each other. Each of the first and second bars382, 384 may also include teeth 383, which may be recessed in order toprevent undesired cutting of items such as surgical gloves. The teeth383 of each of the opposed first and second bars 382, 384 may thenengage each other such that the first and second bars 382, 384 are ableto selectively engage each other to maintain the handle portions 321,351 in a desired position relative to one another. One skilled in theart will appreciate that the locking mechanism described herein is justone of many different locking mechanisms that could be used to maintainthe handle portions 321, 351 in a desired position relative to oneanother.

Now referring to FIGS. 18 and 21, the adjustment mechanism 322 is of asimilar design as the second adjustment mechanism 222 of the instrument210. Thus, the adjustment mechanism 322 may include a threaded portion323 in a location similar to the location of the threaded portion 223 ofthe second adjustment mechanism 222 of the instrument 210 and it mayalso interact with the threaded bore 331 of the housing 329 in a similarmanner as described above with respect to the second adjustmentmechanism 222. Additionally, the alignment feature(s) 335 are configuredin a similar manner as described above for alignment feature(s) 235 ofthe second adjustment mechanism 222, and thus alignment feature(s) 335operate in a similar manner. In the illustrated embodiment, thealignment features 335 are two opposed pins 335, although any otherprotruding structure capable of communicating with the alignment slot(s)333 and the alignment groove(s) 337 may be used.

Like the second adjustment mechanism 222, the adjustment mechanism 322may also be movable relative to the first and/or the second arm 324, 350to adjust the spinal fixation element relative to the bone anchor in asecond direction that is different to, e.g., at an angle to, the firstdirection. Because the adjustment mechanism 322 is so similar to thesecond adjustment mechanism 222, the adjustment mechanism operates in asimilar, removable manner as described above, such that it may be usedeither independently or together with the first and second arms 324,350.

In one embodiment of the instrument 310, the adjustment mechanism 322may be configured to be operably aligned with the longitudinal axis Mrunning through the center of the bone anchor. In another embodiment,the instrument 310 may include the handle portions 321, 351 respectivelybeing oriented to be generally parallel to the adjustment mechanism 322in a plane that is offset from the longitudinal axis M.

While the instruments and methods of the present invention have beenparticularly shown and described with reference to the exemplaryembodiments thereof, those of ordinary skill in the art will understandthat various changes may be made in the form and details herein withoutdeparting from the spirit and scope of the present invention. Those ofordinary skill in the art will recognize or be able to ascertain manyequivalents to the exemplary embodiments described specifically hereinby using no more than routine experimentation. Such equivalents areintended to be encompassed by the scope of the present invention and theappended claims.

The invention claimed is:
 1. An instrument for manipulating a spinal fixation element relative to a bone anchor, the instrument comprising: a first arm having a proximal end and a distal end, the distal end being configured to both engage a first receiving portion of a bone anchor and to direct a spinal fixation element in a direction generally toward a central axis of the instrument and toward a spinal fixation element receiving portion of the bone anchor; a second arm pivotally connected to the first arm such that the first arm and the second arm are pivotable about a pivot axis that intersects the first arm and the second arm, the second arm having a proximal end and a distal end, the distal end being configured to both engage a second receiving portion of the bone anchor and to direct the spinal fixation element generally toward the central axis of the instrument and toward the spinal fixation element receiving portion of the bone anchor; a housing coupled to one of the first arm and the second arm and being disposed between the proximal and distal ends thereof, the housing having a threaded bore disposed therethrough; and an adjustment mechanism movable through the threaded bore and relative to at least one of the first arm and the second arm, the adjustment mechanism being operable to move the spinal fixation element distally with respect to the instrument and toward the spinal fixation element receiving portion of the bone anchor to assist in seating the spinal fixation element in the spinal fixation element receiving portion of the bone anchor, wherein a longitudinal axis along which the adjustment mechanism is configured to move is parallel to and in a different longitudinal plane than a longitudinal plane extending longitudinally through the proximal ends of the first and second arms, and wherein a location at which the housing is coupled to one of the first and second arms is in or adjacent to the longitudinal plane extending longitudinally through the proximal ends of the first and second arms.
 2. The instrument of claim 1, further comprising one or more alignment openings located in the housing, wherein the adjustment mechanism includes one or more alignment features configured to engage one or more of the one or more alignment openings to align the adjustment mechanism with respect to the bone anchor.
 3. The instrument of claim 1, further comprising one or more alignment openings located in distal ends of each of the first and second arms, wherein the adjustment mechanism includes one or more alignment features configured to engage the alignment openings to align the adjustment mechanism with respect to the bone anchor.
 4. The instrument of claim 1, wherein the adjustment mechanism includes a threaded portion configured to engage the threaded bore of the housing.
 5. The instrument of claim 1, further comprising a biasing mechanism configured to bias at least one of the first arm and the second arm to one of an open position and a closed position.
 6. The instrument of claim 5, wherein the biasing mechanism is coupled to the housing and configured to bias the first arm in one of the open position and the closed position.
 7. The instrument of claim 5, further comprising a locking mechanism coupled to at least one of the proximal ends of the first and second arms, the locking mechanism being effective to maintain the proximal ends of the first and second arms in a desired position relative to one another.
 8. The instrument of claim 7, wherein the locking mechanism comprises a rack pivotally mounted on one of the proximal ends of the first and second arms and extending towards the other of the first and second arms, and a pawl located on the other of the proximal ends of the first and second anus, the rack being pivotable between a position in which it can be engaged by the pawl and a position in which it is not engageable by the pawl.
 9. The instrument of claim 8, wherein the rack is pivotably oriented at an angle other than zero relative to a substantially vertical plane that extends through the first and second arms.
 10. The instrument of claim 1, wherein at least one of the proximal ends of the first and second arms is inherently flexible and is capable of storing potential energy as a result of a further closure force applied to the proximal ends of the first and second arms after the distal ends of the first and second arms are engaged with the bone anchor.
 11. The instrument of claim 10, wherein at least one of the proximal ends of the first and second arms is able to move a distance approximately in the range of about 5 millimeters to about 10 millimeters toward the other of the proximal ends of the first and second arms after the distal ends of the first and second arms are engaged with the bone anchor.
 12. The instrument of claim 1, further comprising a locking mechanism coupled to at least one of the proximal ends of the first and second arms, the locking mechanism being effective to maintain the proximal ends of the first and second arms in a desired position relative to one another.
 13. The instrument of claim 12, wherein the locking mechanism further comprises: a first bar having a plurality of teeth disposed thereon, the first bar being coupled to the proximal end of the first arm; and a second bar having a plurality of teeth disposed thereon, the second bar being coupled to the proximal end of the second arm, the teeth of the second bar being opposed to the teeth of the first bar such that the first bar and the second bar can selectively engage each other to maintain the proximal ends of the first and second arms in a desired position relative to one another.
 14. An instrument for manipulating a spinal fixation element relative to a bone anchor, the instrument comprising: a first arm having a proximal end and a distal end, the distal end being longitudinally offset from the proximal end and the distal end being configured to engage a first receiving portion of a bone anchor; a second arm pivotally connected to the first arm such that the firm arm and the second arm are pivotable about a pivot axis that intersects the first arm and the second arm, the second arm having a proximal end and a distal end, the distal end being longitudinally offset from the proximal end and being configured to engage a second receiving portion of a bone anchor; a housing coupled to at least one of the first arm and the second arm at a location adjacent to the pivot axis, the housing having a bore disposed therethrough with a central axis that is longitudinally offset from the proximal ends of the first and second arms and aligned with the distal ends of the first and second arms; and an adjustment mechanism movable through the bore, wherein the first arm the second arm are operable to move the spinal fixation element toward the spinal fixation element receiving portion of the bone anchor in a first direction to assist in seating the spinal fixation element in the spinal fixation element receiving portion of the bone anchor by pivoting the first arm and the second arm about the pivot axis, and wherein the adjustment mechanism is operable to move the spinal fixation element toward the spinal fixation element receiving portion of the bone anchor in a second direction that is generally transverse to the first direction to assist in seating the spinal fixation element in the spinal fixation element receiving portion of the bone anchor by moving the adjustment mechanism distally through the threaded bore, wherein the housing is in a different, longitudinally extending plane than the proximal ends of the first and second arms.
 15. The instrument of claim 14, wherein the bore of the housing is threaded and the adjustment mechanism includes a threaded portion configured to engage the threaded bore.
 16. The instrument of claim 14, further comprising a locking mechanism coupled to at least one of the proximal ends of the first and second arms, the locking mechanism being effective to maintain the proximal ends of the first and second arms in a desired position relative to one another.
 17. The instrument of claim 16, wherein the locking mechanism further comprises: a first bar having a plurality of teeth disposed thereon, the first bar being coupled to the proximal end of the first arm; and a second bar having a plurality of teeth disposed thereon, the second bar being coupled to the proximal end of the second arm, the teeth of the second bar being opposed to the teeth of the first bar such that the first bar and the second bar can selectively engage each other to maintain the proximal ends of the first and second arms in a desired position relative to one another. 